CVE-2026-1356 is a Server-Side Request Forgery (SSRF) vulnerability identified in the WordPress plugin 'Converter for Media – Optimize images | Convert WebP & AVIF' developed by mateuszgbiorczyk. The vulnerability resides in the PassthruLoader::load_image_source function, which improperly handles user-supplied input to fetch image resources. This flaw allows unauthenticated attackers to craft requests that the server will execute, effectively making the server perform arbitrary HTTP requests to internal or external systems. SSRF vulnerabilities are dangerous because they can be used to bypass firewall restrictions, access internal-only services, or manipulate internal APIs that are not exposed externally. In this case, the attacker can potentially query sensitive internal endpoints or modify information if internal services accept such requests. The vulnerability affects all plugin versions up to and including 6.5.1. The CVSS v3.1 base score is 4.8, reflecting network attack vector, high attack complexity, no privileges required, no user interaction, and limited confidentiality and integrity impact but no availability impact. No public exploits have been reported yet, but the vulnerability is publicly disclosed and should be treated seriously. The plugin is widely used in WordPress environments for image optimization and conversion, making the attack surface significant. The lack of a patch at the time of disclosure means organizations must rely on compensating controls until an update is released.

For European organizations, this SSRF vulnerability could lead to unauthorized access to internal services that are otherwise protected by network segmentation or firewalls, potentially exposing sensitive data or enabling further lateral movement within the network. Since the vulnerability allows unauthenticated attackers to initiate requests from the web server, it could be exploited to scan internal networks, access metadata services in cloud environments, or interact with internal APIs that control critical functions. This could compromise confidentiality and integrity of internal systems. Although the CVSS score is medium, the actual impact depends on the internal architecture and the sensitivity of services accessible from the web server. Organizations relying heavily on WordPress with this plugin installed on public-facing sites are at increased risk. The vulnerability does not directly impact availability but could be a stepping stone for more complex attacks. European entities in sectors such as finance, healthcare, and government, which often have strict data protection requirements, could face regulatory and reputational damage if internal data is exposed or altered.

1. Monitor for plugin updates and apply patches immediately once available to remediate the vulnerability. 2. Until a patch is released, disable or remove the vulnerable plugin from WordPress installations to eliminate the attack vector. 3. Implement strict egress filtering on web servers hosting WordPress to restrict outbound HTTP requests only to trusted destinations, preventing SSRF exploitation. 4. Use Web Application Firewalls (WAFs) with rules designed to detect and block SSRF attack patterns targeting the plugin’s endpoints. 5. Conduct internal network segmentation to minimize the exposure of sensitive internal services to the web server. 6. Audit and monitor logs for unusual outbound requests originating from the web server to detect potential exploitation attempts. 7. Employ security plugins or tools that can detect anomalous behavior in WordPress environments. 8. Educate administrators about the risks of SSRF and the importance of timely patching and network controls.